fix(health): M2.16 review nit — real idempotency guard for SiteEventLog health bridge (#30)

AddSiteEventLogHealthMetricsBridge registered via AddHostedService(factory-lambda), which sets ImplementationFactory and leaves ImplementationType null. The prior ImplementationType == guard was therefore silently dead — a second call would spin up a second SiteEventLogFailureCountReporter. Fix: add a private SiteEventLogHealthMetricsBridgeMarker singleton and guard on its ServiceType instead. Also corrects the cycle-path comment in both ServiceCollectionExtensions.cs and SiteEventLogFailureCountReporter.cs: StoreAndForward.csproj does reference SiteEventLogging.csproj, so the transitive path HealthMonitoring → StoreAndForward → SiteEventLogging is real, but adding a direct HealthMonitoring → SiteEventLogging reference would NOT create a cycle (SiteEventLogging has no back-edge to HealthMonitoring). The Func<long> seam is a coupling-avoidance measure, not a cycle-breaker. Adds AddSiteEventLogHealthMetricsBridgeTests.AddSiteEventLogHealthMetricsBridge_IsIdempotent_DoesNotDoubleRegister_HostedService as a regression test (builds provider and asserts exactly one reporter via GetServices<IHostedService>().OfType<T>()).
2026-06-16 07:22:35 -04:00
parent d81f747434
commit c9244d8bda
4 changed files with 94 additions and 22 deletions
@@ -0,0 +1,48 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests;
+
+/// <summary>
+/// M2.16 (#30) idempotency regression — code-review finding on commit d81f747.
+/// <para>
+/// <see cref="ServiceCollectionExtensions.AddSiteEventLogHealthMetricsBridge"/> uses a
+/// factory-lambda overload of <c>AddHostedService</c>, which sets only
+/// <c>ImplementationFactory</c> and leaves <c>ImplementationType</c> null.  The original
+/// <c>ImplementationType ==</c> guard was therefore a silent no-op: a second call would spin
+/// up a second <see cref="SiteEventLogFailureCountReporter"/> (two timers both polling).
+/// The fix uses a private marker singleton whose <c>ServiceType</c> is always set.
+/// </para>
+/// </summary>
+public class AddSiteEventLogHealthMetricsBridgeTests
+{
+    [Fact]
+    public void AddSiteEventLogHealthMetricsBridge_IsIdempotent_DoesNotDoubleRegister_HostedService()
+    {
+        // M2.16 (#30): calling the bridge method twice must register exactly one
+        // SiteEventLogFailureCountReporter. Without the marker-type guard the
+        // ImplementationType == check was a no-op for factory-lambda registrations,
+        // so the second call would have added a second hosted service (two timers).
+        var services = new ServiceCollection();
+        services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
+        services.AddSingleton(typeof(ILogger<>), typeof(NullLogger<>));
+        services.AddHealthMonitoring();
+
+        Func<IServiceProvider, Func<long>> factory = _ => () => 0L;
+
+        services.AddSiteEventLogHealthMetricsBridge(factory);
+        services.AddSiteEventLogHealthMetricsBridge(factory);
+
+        // Count IHostedService descriptors whose factory produces a
+        // SiteEventLogFailureCountReporter. Because it is factory-registered,
+        // ImplementationType is null — we count by resolving and checking type.
+        using var provider = services.BuildServiceProvider();
+        var reporters = provider.GetServices<IHostedService>()
+            .OfType<SiteEventLogFailureCountReporter>()
+            .ToList();
+
+        Assert.Single(reporters);
+    }
+}